In a production process of a semiconductor element, by using an original image pattern (that is, a mask or a reticle, hereinafter collectively referred to as a mask) in which a circuit pattern is formed, the pattern is exposed and transferred onto a wafer by a reduction projection exposure apparatus, called a stepper or a scanner, to form a circuit on the wafer, thereby producing a semiconductor element.
With high integration and large capacity of recent Large Scale Integration (LSI), a circuit dimension required for a semiconductor element has become increasingly narrowed. Thereby high accuracy is required for a pattern formed in a mask. Accordingly it is necessary to detect a defect of an extremely small pattern in a mask inspection. Japanese Patent No. 4236825 discloses an example of the conventional inspection apparatus.
In order to accurately inspect a pattern formed in a mask, it is necessary to accurately measure a position coordinate of the pattern over the whole surface of the mask. It is also necessary to measure the position coordinate of the pattern in the mask, to obtain a distribution map of a misplacement amount between the measurement value of a position coordinate and a design position coordinate, and to feed back the distribution map to a mask producing process.
Conventionally, the position coordinate of a mark arranged around the pattern is measured with a dedicated position measuring apparatus such as a CD-SEM, and the position coordinate of the pattern is predicted from the measurement value of a position coordinate of the mark to perform the inspection. However, there are few marks because the space where the mark can be arranged on the surface of the mask is restrictive. Accordingly there is a problem in that the position coordinate of the pattern may not be accurately obtained over the whole surface of the mask.
There is also a known method for acquiring the position coordinate of the pattern, using an image for inspecting that is acquired by a pattern inspection apparatus. In this method, based on an optical image of the mask pattern, the position coordinate of the pattern is obtained by referring to a reference image that is generated from the design pattern. However, because this process is performed during an inspection process, a fluctuation of the measurement value of a position coordinate of the pattern may be generated as a result of, thermal expansion of the mask irradiated with inspection light for a long time, a fluctuation of an air flow in the inspection apparatus, or a measurement error of a length measuring system due to various heat sources of the inspection apparatus.
Further, it is conceivable that the position coordinate of the pattern obtained from the image obtained in the inspection process is corrected using the position coordinate measured with the position measuring apparatus. However, because the position measured with the position measuring apparatus is locally determined, as described above, the position coordinate of the pattern arranged in a non-measured region is insufficiently corrected.
The present invention has been devised to solve the problem described above. An object of the present invention is to provide a position measuring method for being able to accurately obtain the position of the pattern to be inspected.
Another object of the present invention is to provide a method for producing an accurate misplacement map associated with the position of the pattern to be inspected.
Another object of the present invention is to provide an inspection system that can generate an accurate misplacement map associated with the position of the pattern to be inspected.
Further, other objects and advantages of the present invention are apparent from the following description.